High-frequency heating of the solar wind triggered by low-frequency turbulence

The fast solar wind’s high speeds and non-thermal features require that considerable heating occurs well above the Sun’s surface. Two leading theories seem incompatible: low-frequency ‘Alfvénic’ turbulence, which transports energy outwards is observed ubiquitously by spacecraft but seems insufficient to explain dominance of ion over electron heating; high-frequency ion-cyclotron waves, ions lack an obvious source. Here we argue recently proposed ‘helicity barrier’ effect, limits inhibiting turbulent cascade smallest scales, can unify these two paradigms. Our six-dimensional simulations show how helicity barrier causes large-scale grow through time, generating small parallel scales ion-cyclotron-wave from while simultaneously explaining various other long-standing observational puzzles. predicted causal link between plasma expansion ion-to-electron ratio suggests could contribute key differences slow wind streams. mechanism transfer Alfvénic into waves in atmosphere, playing a role solar-wind wind.